Interleukin-1 (IL-1) is a major pro-inflammatory and immunoregulatory protein that stimulates fibroblast differentiation and proliferation, the production of prostaglandins, collagenase and phospholipase by synovial cells and chondrocytes, basophil and eosinophil degranulation and neutrophil activation. Oppenheim, J. H. et al, Immunology Today, 7, pp. 45-56 (1986). As such, it is involved in the pathogenesis of chronic and acute inflammatory and autoimmune diseases. For example, in rheumatoid arthritis, IL-1 is both a mediator of inflammatory symptoms and of the destruction of the cartilage proteoglycan in afflicted joints. Wood, D. D. et al., Arthritis Rheum. 26, 975, (1983); Pettipher, E. J. et al., Proc. Natl. Acad. Sci. USA 71, 295 (1986); Arend, W. P. and Dayer, J. M., Arthritis Rheum. 38, 151 (1995). IL-1 is also a highly potent bone resorption agent. Jandiski, J. J., J. Oral Path 17, 145 (1988); Dewhirst, F. E. et al., J. Immunol. 8, 2562 1985). It is alternately referred to as “osteoclast activating factor” in destructive bone diseases such as osteoarthritis and multiple myeloma. Bataille, R. et al., Int. J. Clin. Lab. Res. 21(4), 283 (1992). In certain proliferative disorders, such as acute myelogenous leukemia and multiple myeloma, IL-1 can promote tumor cell growth and adhesion. Bani, M. R., J. Natl. Cancer Inst. 83, 123 (1991); Vidal-Vanaclocha, F., Cancer Res. 54, 2667 (1994). In these disorders, IL-1 also stimulates production of other cytokines such as IL-6, which can modulate tumor development (Tartour et al., Cancer Res. 54, p. 6243 (1994). IL-1 is predominantly produced by peripheral blood monocytes as part of the inflammatory response and exists in two distinct agonist forms, IL-1α and IL-1β. Mosely, B. S. et al., Proc. Nat. Acad. Sci., 84, pp. 4572-4576 (1987); Lonnemann, G. et al., Eur. J. Immunol., 19, pp. 1531-1536 (1989).
IL-1β is synthesized as a biologically inactive precursor, pro-IL-1β. Pro-IL-1β lacks a conventional leader sequence and is not processed by a signal peptidase. March, C. J., Nature, 315, pp. 641-647 (1985). Instead, pro-IL-1β is cleaved by interleukin-1β converting enzyme (ICE) between Asp-116 and Ala-117 to produce the biologically active C-terminal fragment found in human serum and synovial fluid. Sleath, P. R., et al., J. Biol. Chem., 265, pp. 14526-14528 (1992); A. D. Howard et al., J. Immunol., 147, pp. 2964-2969 (1991). ICE is a cysteine protease localized primarily in monocytes. It converts precursor IL-1β to the mature form. Black, R. A. et al., FEBS Lett., 247, pp. 386-390 (1989); Kostura, M. J. et al., Proc. Natl. Acad. Sci. U.S.A., 86, pp. 5227-5231 (1989). Processing by ICE is also necessary for the transport of mature IL-162  through the cell membrane.
ICE (or caspase-1) is a member of a family of homologous enzymes called caspases. These homologs have sequence similarities in the active site regions of the enzymes. Such homologs (caspases) include TX (or ICErel-II or ICH-2) (caspase-4) (Faucheu, et al., EMBO J., 14, p. 1914 (1995); Kamens J., et al., J. Biol. Chem., 270, p. 15250 (1995); Nicholson et al., J. Biol. Chem., 270 15870 (1995)), TY (or ICErel-III) (caspase-5) (Nicholson et al., J. Biol. Chem., 270, p. 15870 (1995); ICH-1 (or Nedd-2) (caspase-2) (Wang, L. et al., Cell, 78, p. 739 (1994)), MCH-2 (caspase-6), (Fernandes-Alnemri, T. et al., Cancer Res., 55, p. 2737 (1995), CPP32 (or YAMA or apopain) (caspase-3) (Fernandes-Alnemri, T. et al., J. Biol. Chem., 269, p. 30761 (1994); Nicholson, D. W. et al., Nature, 376, p. 37 (1995)), CMH-1 (or MCH-3) (caspase-7) (Lippke, et al., J. Biol. Chem., 271(4), p1825-1828 (1996)); Fernandes-Alnemri, T. et al., Cancer Res., (1995)), Mch5 (caspase-8) (Muzio, M. et. al., Cell 85(6), 817-827, (1996)), MCH-6 (caspase-9) (Duan, H. et. al., J. Biol. Chem., 271(34), p. 16720-16724 (1996)), Mch4 (caspase-10) (Vincenz, C. et. al., J. Biol. Chem., 272, p. 6578-6583 (1997); Fernandes-Alnemri, T. et. al., Proc. Natl. Acad. Sci. 93, p. 7464-7469 (1996)), Ich-3 (caspase-11) (Wang, S. et. al., J. Biol. Chem., 271, p. 20580-20587 (1996)), mCASP-12 (caspase-12), (Van de Craen, M. et. al., FEBS Lett. 403, p. 61-69 (1997); Yuan, Y. and Miura, M. PCT Publication WO95/00160 (1995)), ERICE (caspase-13), (Humke, E. W., et. al., J. Biol. Chem., 273(25) p. 15702-15707 (1998)), and MICE (caspase-14) (Hu, S. et. al., J. Biol. Chem., 273(45) p. 29648-29653 (1998)).
Each of these ICE homologs, as well as ICE itself, is capable of inducing apoptosis when overexpressed in transfected cell lines. Inhibition of one or more of these homologs with the peptidyl ICE inhibitor Tyr-Val-Ala-Asp-chloromethylketone results in inhibition of apoptosis in primary cells or cell lines. Lazebnik et al., Nature, 371, p. 346 (1994).
Caspases also appear to be involved in the regulation of programmed cell death or apoptosis. Yuan, J. et al., Cell, 75, pp. 641-652 (1993); Miura, M. et al., Cell, 75, pp. 653-660 (1993); Nett-Fiordalisi, M. A. et al., J. Cell Biochem., 17B, p. 117 (1993). In particular, ICE or ICE homologs are thought to be associated with the regulation of apoptosis in neurodegenerative diseases, such as Alzheimer's and Parkinson's disease. Marx, J. and M. Baringa, Science, 259, pp. 760-762 (1993); Gagliardini, V. et al., Science, 263, pp. 826-828 (1994). Inhibition of caspases have also recently been shown to be effective in a murine model of amylotropic lateral sclerosis. Li, M. et al.; Science, 288, pp. 335-339 (2000). Therapeutic applications for inhibition of apoptosis may include, among others, treatment of Alzheimer's disease, Parkinson's disease, stroke, myocardial infarction, spinal atrophy, and aging.
ICE has been demonstrated to mediate apoptosis (programmed cell death) in certain tissue types. Steller, H., Science, 267, p. 1445 (1995); Whyte, M. and Evan, G., Nature, 376, p. 17 (1995); Martin, S. J. and Green, D. R., Cell, 82, p. 349 (1995); Alnemri, E. S., et al., J. Biol. Chem., 270, p. 4312 (1995); Yuan, J. Curr. Opin. Cell Biol., 7, p. 211 (1995). A transgenic mouse with a disruption of the ICE gene is deficient in Fas-mediated apoptosis (Kuida, K. et al., Science 267, 2000 (1995)). This activity of ICE is distinct from its role as the processing enzyme for pro-IL-1β. It is conceivable that in certain tissue types, inhibition of ICE may not affect secretion of mature IL-1β, but may inhibit apoptosis.
Enzymatically active ICE has been previously described as a heterodimer composed of two subunits, p20 and p10 (20 kDa and 10 kDa molecular weight, respectively). These subunits are derived from a 45 kDa proenzyme (p45) by way of a p30 form, through an activation mechanism that is autocatalytic. Thornberry, N. A. et al., Nature, 356, pp. 768-774 (1992). The ICE proenzyme has been divided into several functional domains: a prodomain (p14), a p22/20 subunit, a polypeptide linker and a p10 subunit. Thornberry et al., supra; Casano et al., Genomics, 20, pp. 474-481 (1994).
Full length p45 has been characterized by its cDNA and amino acid sequences. PCT patent applications WO 91/15577 and WO 94/00154. The p20 and p10 cDNA and amino acid sequences are also known. Thornberry et al., supra. Murine and rat ICE have also been sequenced and cloned. They have high amino acid and nucleic acid sequence homology to human ICE. Miller, D. K. et al., Ann. N.Y. Acad. Sci., 696, pp. 133-148 (1993); Molineaux, S. M. et al., Proc. Nat. Acad. Sci., 90, pp. 1809-1813 (1993). The three-dimensional structure of ICE has been determined at atomic resolution by X-ray crystallography. Wilson, K. P., et al., Nature, 370, pp. 270-275 (1994). The active enzyme exists as a tetramer of two p20 and two p10 subunits.
Recently, ICE and other members of the ICE/CED-3 family have been linked to the conversion of pro-IL-18 to IL-18 or to the production of IFN-γ in vivo (PCT application PCT/US96/20843, publication no. WO 97/22619, which is incorporated herein by reference). IL-18 is synthesized in vivo as the precursor protein “pro-IL-18”.
Interleukin-18 (IL-18), formerly interferon-gamma inducing factor, (IGIF) is an approximately 18-kDa polypeptide that stimulates T-cell production of interferon-gamma (IFN-γ-). IL-18 is produced by activated Kupffer cells and macrophages in vivo and is exported out of such cells upon endotoxin stimulation. Like IL-1β, IL-18 is synthesized as a biologically inactive precursor molecule lacking a single peptide, which requires cleavage into an active, mature molecule by IL-1β converting enzyme. Dinerello, C. A. Methods, 19, pp 121-132 (1999). Thus, a compound that decreases IL-18 production would be useful as an inhibitor of such T-cell stimulation which in turn would reduce the levels of IFN-γ production by those cells.
IFN-γ is a cytokine with immunomodulatory effects on a variety of immune cells. In particular, IFN-γ is involved in macrophage activation and Th1 cell selection (F. Belardelli, APMIS, 103, p. 161 (1995)). IFN-γ exerts its effects in part by modulating the expression of genes through the STAT and IRF pathways (C. Schindler and J. E. Darnell, Ann. Rev. Biochem., 64, p. 621 (1995); T. Taniguchi, J. Cancer Res. Clin. Oncol., 121, p. 516 (1995)).
Mice lacking IFN-γ or its receptor have multiple defects in immune cell function and are resistant to endotoxic shock (S. Huang et al., Science, 259, p. 1742 (1993); D. Dalton et al., Science, 259, p. 1739 (1993); B. D. Car et al., J. Exp. Med., 179, p. 1437 (1994)). Along with IL-12, IL-18 appears to be a potent inducer of IFN-γ production by T cells (H. Okamura et al., Infection and Immunity, 63, p. 3966 (1995); H. Okamura et al., Nature, 378, p. 88 (1995); S. Ushio et al., J. Immunol., 156, p. 4274 (1996)).
IFN-γ has been shown to contribute to the pathology associated with a variety of inflammatory, infectious and autoimmune disorders and diseases. Thus, compounds capable of decreasing IFN-γ production would be useful to ameliorate the effects of IFN-γ related pathologies.
Accordingly, compositions and methods capable of regulating the conversion of pro-IL-18 to IL-18 would be useful for decreasing IL-18 and IFN-γ production in vivo, and thus for ameliorating the detrimental effects of these proteins which contribute to human disorders and diseases.
Caspase inhibitors represent a class of compounds useful for the control of inflammation or apoptosis or both. Peptide and peptidyl inhibitors of ICE have been described (PCT patent applications WO 91/15577, WO 93/05071, WO 93/09135, WO 93/12076, WO 93/14777, WO 93/16710, WO 95/35308, WO 96/30395, WO 96/33209 and WO 98/01133; European patent applications 503 561, 547 699, 618 223, 623 592, and 623 606; and U.S. Pat. Nos. 5,434,248, 5,710,153, 5,716,929, and 5,744,451). Such peptidyl inhibitors of ICE have been observed to block the production of mature IL-1β in a mouse model of inflammation (vide infra) and to suppress growth of leukemia cells in vitro (Estrov et al., Blood, 84, 380a (1994)). However, due to their peptidic nature, such inhibitors are typically characterized by undesirable pharmacologic properties, such as poor cellular penetration and cellular activity, poor oral absorption, instability and rapid metabolism. Plattner, J. J. and D. W. Norbeck, in Drug Discovery Technologies, C. R. Clark and W. H. Moos, Eds. (Ellis Horwood, Chichester, England, 1990), pp. 92-126. These properties have hampered their development into effective drugs.
Non-peptidyl compounds have also been reported to inhibit ICE in vitro. PCT patent application WO 95/26958; U.S. Pat. No. 5,552,400; Dolle et al., J. Med. Chem., 39, pp. 2438-2440 (1996). It is not clear however whether these compounds have the appropriate pharmacological profiles to be therapeutically useful.
WO 99/47545 describes a novel class of caspase inhibitors reported to have a favorable in vivo profile. These inhibitors are represented by the formula:
where X, Y, and R1-R6 are various substituents. Among the many examples of this class of inhibitors, the following structure was disclosed:

As is known in the art, the bioavailability of compounds within a structural class is difficult to predict. Relatively minor structural modifications often have a large impact on the absorption of a compound, its blood level concentrations and/or its half-life. For example, such variations in bioavailability can be seen from the data in WO 99/47545. As a consequence, structurally related compounds that have very good in vitro potency may vary in therapeutic effectiveness.
Though progress has been made in improving the bioavailability of ICE inhibitors, there continues to be a need to identify and develop compounds that can effectively inhibit caspases, and that have improved in vivo activity. Such compounds would be useful as agents for preventing and treating chronic and acute forms of IL-1-, apoptosis-, IL-18-, or IFN-γ-mediated diseases, as well as inflammatory, autoimmune, destructive bone, proliferative, infectious, or degenerative diseases.